How can i update my changes in the UI scripts?
One option is to run the altered script while it is in blender's text editor. There is a button in the text editor header for this.

Another option is to save the changes to disk and press F8. This will have blender re-run all the interface and addon scripts similar to having re-started blender, which is also an option.

Having said that it isn't recommended to alter the scripts that come with blender. You can create an addon that alters or adds to existing menus and lets you easily turn it on/off as well as use it again in the next version after you update.

If you look at some existing addons you can easily work out that you can add to the object specials menu with a line such as bpy.types.VIEW3D_MT_object_specials.append(MyMenu)